Variables and Functions Chapter 3 3-1. Variables Named storage location in computer’s memory...
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Transcript of Variables and Functions Chapter 3 3-1. Variables Named storage location in computer’s memory...
Variables Named storage location in computer’s
memory Programs may need to store data when
running Types of data that can be stored
o Local variableso Parameter variableso Class-level variableso World-level variables
3-2
Variable Types Local variables
o Belongs to a specific methodo Only used in that methodo Variables cease to exist when method stopso Will be talked about today
Parameter variableso Holds argument that is passed to a called method
Class-level variableso It is like a property and belongs to a specific object
World-level variableso It is a world-level property
3-3
Creating Local Variables Local variables belong to
a specific method (such as world.my first method)
Create variable by clicking on create new variable in desired method
Variables require 3 thingso Nameo Typeo Initial value
3-4
name
type
value
Variable Definition Variable Names
o Must be unique within the method or objecto Should be meaningful and reflect the variable’s
purposeo Named using camelCase
Variable Typeso Numbers, Boolean, Objects, Other (such as
String, Color, Sound, etc.)
Initial Valueo Value initially stored in the variable
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Variables
Tile appearance shows the type of variable
Numbers Boolean Objects String Variable declaration - creating a variable
3-6
Variable Assignment
Variables have an initial value Initial value held until a different value is
assigned New values can be
assigned while the method is runningo Use Set instructionso Done by dragging variable tile into Methods
Editor
3-7
Review What is a variable? What are three things that must be specified
when creating a new variable? Where in the Method Editor do variable tiles
appear? What do the characters 123 appearing on a
variable tile tell you? What do characters abc on a variable tile tell
you? How do you create a set instruction for a
variable? 3-8
Function Asks a question to
o Check a conditiono Compute a value
Used to get information about…o Size of objects
What is snowwoman's height?
o Relationship of one object to another What is distance between lunar robot and rock?
Used to get other informationo Timeo Ask user for information
Value What a function returns after it
o Asks questiono Or performs a computation
Type of value depends on kind of functiono distance to returns a numbero is to the left of returns a Boolean value
Number valueo Whole number ex: 3 meterso Fractional value, ex: 1.2 meterso In lunar example
What is distance of robot to rock?
Function vs. Method Functions
o Perform calculationso Determine state of an object or systemo Return a value
Methods perform an action
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Types of Values Number
o 3, or 1.3 Boolean
o true, false String
o “Slithy Toves?” Object
o lunarRobot, alien Position in world
o (0, 0, 0) – (x,y,z) center of an Alice world
World Level Primitive Functions List of world level functions categories
o Boolean logico Matho Randomo Stringo Ask usero Mouseo Timeo Advanced matho Other
3-13
Asking User for Input
World has three primitive functions that ask for user input
Each question is shown in a dialog box Ask user for a number
User enters a number
Ask user for yes or no User clicks on yes or no
Ask user for a string User answers with words
or a sentence
3-14
Class Primitive Object Functions Objects have different
primitive functions from the world level
Class level functionso Proximityo Sizeo Spatial relationo Point of viewo Other
Object primitive proximity functions
Using Function distance to
Built-in distance to function o Determines distance from center of one
object to center of another objecto Better than guessing distance to object
An Alice function is not a "stand-alone" instructiono It is nested within another instruction
Review What makes a function different from a
method? How do you see a list of functions an object
has? What are the three primitive world functions
that ask the user to input a value? What are some class level functions? What does the primitive distance to function
do?
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